EPR Study of the Ferroelastic Transition in KD₃(SeO₃)₂

Abstract

Electron paramagnetic resonance spectra of the SeO₂⁻ centers in KD₃(SeO₃)₂ demonstrate that the phase transition in this system is associated with an ordering of the O–H(2)– –O hydrogens and a small rotation of the SeO₃ groups around the a-axis with the angle of rotation being proportional to the order parameter. The ferroelastic transition is thus triggered by a soft optic deuteron-lattice mode of B_3g symmetry inducing the acoustic C₄₄ instability.